Skeleton Key
by Sirianna-Black
Summary: Jace and the team are on the hunt looking for some vampires that have broken the accords - while on the hunt they meat someone unexpected .
1. Chapter 1 Chasing Shadows

**THE TITLE : **Skeleton Key

**THE RATING **: Teen +

**THE GENRE :** All / Romance

**THE TYPE :** Crossover

**CROSSOVER :** The Mortal Instruments / Buffy the Vampire Slayer

**KEY PAIRINGS :** Jace / OC

**SUMMARY :** Jace and the team are on the hunt looking for some vampires that have broken the accords - while on the hunt they meat someone unexpected .

**DISCLAIMER : **I do not own canon content of anything from The Mortal Instruments or Buffy the Vampire slayer - I mearely own the plot for this story and any original content within it.

**AUTHORS NOTES :** I just want to let everyone know I have only read City of Bones and just started on City of Ashes, this idea came to me while reading and watching buffy the vampire slayer, I apologize in advance for any errors i make with anything involving The Mortal Instruments series. But this is my own story/idea so things won't be a 100 % canon - but fanfiction is meant to be not canon. So my story is taking place Post - City of Bones. Also most of you may also know that City Of Bones will be turned into a film you may agree or not agree on their casting but personally I am 50/50 with their choices in casting so I will leave canon characters up to your imaginations - as for my story, and my lead original character Aderes will be portrayed by: "Taylor Momsen." - If you don't know her you can google her or search her in whatever way you search.

**I .) CHASING SHADOWS**

**The clatter of feet on the cement ground **sounded from an alley behind a newly opened club that was packed beyond the brim with people, with people still be waiting to be let inside, but the sounds of fighting and scattering in the alley were drowned out by the usual new york noise and the sounds coming from within the club that was dubbed "Spirits". The blond currently in the alley fighting off several Children of Lilith had been enjoying the new club and what it had to offer - but that had been cut short when her "vampy senses" started tingling and alerted her to the blood suckers that had been in the club - They must have charmed their way in because they were in now way passable for teenagers. Her pale skin was smeared with grime of the alley, cuts mixed in with the dirt and blood - she was some sight to clothes torn and ripped as she jumped back into the fray of the fight, not about to let a few fanged asses get the upper-hand and slip away from her. If it were a normal day, she just looked like trouble with an attitude problem.

Aderes however could pass for a girl sweet and innocent if she happened to change her wardrobe and stuck a few berets in her hair and wiped off some of the make up she wore. But she appeared either way to be a normal girl either who took the wrong path and went to the wrong side to the tracks... Which was half true but not the complete story. Aderes wasn't your everyday teenager, she was a slayer of all things that were bad. Vampires being one of them. She was granted with the gift to roam graveyards at night instead of the theater with her friends. Not that she had many friends. She kept people at a distance, The blond couldn't risk people finding out her nighttime pastime. As usual though her attempt to be normal was cast down the drain by a couple of hungry blood suckers.

"Why for once can't you jackasses stay in your coffins?" She asked looking at them and sighed, "you actually think your scary.. I mean seriously is that a lace collar? Man you're way out of date with your clothes."

She said looking at them. The vampires couldn't help but look at her the one with the lace collar looking down at it then back at her and tilting its head. The four were confused. She seemed like an ordinary mundane, She was no shadow hunter yet something about her set them on edge. Put them on guard. The didn't know how she had managed to lure them out of the club through the back. They had though she was and easy meal till she had turned one of their friends to dust, which was now scattered and couldn't be differentiated between the loose gravel and dirt on the ground due to the scuffling and fighting that had been occurring between them. She had power beyond what someone who appeared to be a mundane should not have - They had tossed her into a wall and she got up like it was barely nothing, as if it had just been a paper cut. The suspected her to drop where she stood, she should have been exhausted but she stood before them barely out of breath. Mocking them - It was unsettling.

* * *

**Clary had been standing in line with **Simon, Isabelle, Alec, and her new found brother, Jace for the past hour waiting to get in. Isabelle was less than please that they had to wait and was grumbling about not getting there earlier to be closer to the front of the line. The Five of them were debating on leaving and coming back the next night, in hopes the crowd wouldn't be so bad and they could get in earlier by arriving earlier and waiting just as long for the doors to open. Clary rolled her eyes she was getting tired of Isabelle's ranting but she was sure all of them were, her assumptions were proved correct when Jace told her to shut it causing Isabelle to give him a dirty look before the five of them stepped out of line figuring they could find something much better to do than wait in line till most likely closing time.

"Really Jace, you're looking for demons now?"

Alec asked giving his parabatai, a strange look even though he had a good idea what Jace would say in return to him, because that was his way of thinking and they all knew it.

"What, when there is nothing better to do. Find Demons."

Jace remarked to Alec as they walked down the street stopping near the Alley when the sensor went off, and he continued speaking,

"Ah just what we're looking for."

As they headed toward the Alley the scuffling within became evident to their ears and the shadow hunters withdrew their Stele's, Clary holding out the witchlight so they could see. The bright light igniting the alley with a blaze of colors. They could see the fight going on and to their eyes it appeared to be a mundane fighting with three vampires. The three shadow hunters did not speak or form a plan they sprung into action as Clary and Simon hung back, Clary holding the witchlight high to keep the Ally well lit, but by the time the Shadow hunters even grew close to the fight, the blond they believed to be a mundane had slain the vampires and stood, stake in hand only looking away from the dust at those she now realized were in the ally with her.

"How the hell did you - ?"

Alec was the first to speak and Clary and Simon joined the group of shadow hunters as Aderes raised an eyebrow at them,

"You act like you've never seen a girl slay something before."

She said and gave a smirk before turning to grab her bag and leather coat. Ignoring the pain from the cuts scrapes and dug in gravel that covered every inch of uncovered skin, which tonight was a lot as she hadn't planned on slaying, even though as always she came well prepared. But she did not give the group time to speak, nor did she say more. She took up the fire escape and even though Jace and Alec followed when they arrived the roof top was empty. As if she had been a shadow, and hadn't existed.

**CLOSING STATEMENT :** I hope you enjoyed the first chapter, reviews mean a continuation of this story. so please review / comment and i will surely continue.


	2. Chapter 2 Chinese Burn

**THE TITLE : **Skeleton Key

**THE RATING **: Teen +

**THE GENRE :** All / Romance

**THE TYPE :** Crossover

**CROSSOVER :** The Mortal Instruments / Buffy the Vampire Slayer

**KEY PAIRINGS :** Jace / OC

**SUMMARY :** Jace and the team are on the hunt looking for some vampires that have broken the accords - while on the hunt they meat someone unexpected .

**DISCLAIMER : **I do not own canon content of anything from The Mortal Instruments or Buffy the Vampire slayer - I merely own the plot for this story and any original content within it.

**AUTHORS NOTES :** I just want to let everyone know I have only read City of Bones and just started on City of Ashes, this idea came to me while reading and watching Buffy the vampire slayer, I apologize in advance for any errors i make with anything involving The Mortal Instruments series. But this is my own story/idea so things won't be a 100 % canon - but fanfiction is meant to be not canon. So my story is taking place Post - City of Bones. Also most of you may also know that City Of Bones will be turned into a film you may agree or not agree on their casting but personally I am 50/50 with their choices in casting so I will leave canon characters up to your imaginations - as for my story, and my lead original character Aderes will be portrayed by: "Taylor Momsen." - If you don't know her you can google her or search her in whatever way you search.

**II .) CHINESE BURN**

**The Shadows hunters didn't know **what to think about the girl in the alley who had turned three vampires into dusts and then booked it from the alley and was gone as if she had never existed. They sat at the institute trying to figure it out, but none of them could come to a conclusion. They had come up with some of the most ridiculous of things such as a vampire with a grudge on her own kind, or some form of demon, but nothing they named sticked.

"So she wasn't one of you then?"

Simon asked and Alec shook his head along with the other three, who followed suit in the head shaking before he spoke,

"No she couldn't have been she didn't have the marks, besides no other shadow hunters were suppose to be coming this way- Its just us."

He explained, Shadow hunter had been ruled out quickly before Simon had even brought it up. She had no marks, she wasn't giving off anything to say she was anything out of the ordinary, to say she was a downworlder - she looked like a mundane, but none of them had ever seen a mundane move so fast or kill vampires with such ease... they doubted that she was just a mundane as she had appeared to be but they had no evidence or anything saying she was something out of the ordinary. They had turned the alley upside down and found nothing except alley garbage and signs of the struggle and a bit of blood here and there which did them no good.

"Well maybe we should go back. Maybe she'll show up again?"

Clary suggested from where she sat by Simon. It was a suggestion, and it was more than anyone else was putting on the table, and Jace and the Others were demanding to know who she was... and what she was.

"Look for anyone who has looked like they were thrown around an Alley because she looked pretty beat from what I seen."

Isabelle interjected agreeing with Clary's plan, Seeing as it was the only card on the table and fitted in what they were planning to do any how.

* * *

**The blonde had made it home **and she was worn out, the vampires had put up a good fight and in the end lost but she was going to feel it in the morning. She walked through the front door shutting it behind her and threw down her bag and jacket and began peeling off her clothing as she headed to the bathroom. She needed to clean up. Aderes looked like Hell, like she had been dragged through a cactus field backwards. She felt like it to. Wincing she peeled off her last layer and started a bath. Just what she needed a relaxing bath to extract the grime from her with before bed. She grabbed her usual kit and sat it on the edge of the clawed foot tub. and once she sank down in the heated water pulled out the tweezers and began extracting glass and gravel from the cuts and gouges she had on her body from the fight.

Aderes sat in the water till it was pink from blood and swirling with dirt and grew to cold for her liking before standing and getting out, toweling off and changing. she grabbed a quick dinner and ate just as fast before she went to her room and crawling in bed, a stake under her pillow and a knife on her bedside table just in case, even though all her doors and windows were locked and she had made sure of it, so as to prevent unwanted visitors. Even if she was always ready for them.

* * *

**Morning came quickly for those **at the institute and it wasn't long after breakfast that Clary and Simon arrived. They were regulars at the institute seeing as Clary was Jace's sister and Simon a close friend to the group. They sat around the dining room table discussing the situation at hand and how to handle it if things didn't go smoothly. All intending to go well prepared for just about anything that may arise from their unknown new friend.

The day went by in a whirl wind of discussion and raiding of the armory before it came time to head back to the club. The group was anxious and it showed they arrived and got in quickly and began scoping the area while blending in with the growing crowd, staying within ear shot of each other. Hours ticked by and they began to think it was going to be a waste of time they could have been spending on something else but soon their waiting paid off, She walked through the door, looking unscathed and a better sight than what she had been, "That's her." Isabelle confirmed as they watched from where they all sat at a table. One of those high ones with the bar stools at it.

* * *

**Aderes had started to not revisit **the cub so soon - the night before replayed in her mind, the people who had chased after her from the alley. She did not know who or what they were and they seemed to interested in her for her liking. She wasn't sure what they were and by the looks they had given her before she had fled the alley like a monkey out of a canon, they didn't know what she was either. She wanted to keep it that way even though curiosity was like a demon locked in a closet, like an animal in tis cage telling her otherwise. But she had gone against what she would consider better judgement and went to the club anyways.

She had walked in as always scoping it for things she could slay as she did, like she did with every building she entered. She grabbed a "minor friendly" drink from the bar and made her way to a table for the time being and took a seat. Enjoying the thrum of the music and the over head lights while she sipped at the soda she had gotten. Only standing unaware at the moment of being watched and headed to the dance floor losing herself in the crowd. She had completely lost herself in the thrum of the music till she felt someone come up behind her causing her to go rigid.

"That was pretty smooth work you did in that alley last night."

The voice obviously male said to her, as she looked around she became aware of four other sets of eyes watching her, she kept her cool though, "Meet me out back and I'll lay some of it on you." She snapped and with a swift kick landed her foot against the guy's knee cap and fled to the back where she knew she could fight without interuptions. Jace groaned as he was kicked but recovered before going quickly with the others to the back exit and found the girl waiting armed with a metal rod. Aderes barely gave them time to get into the alley before she spoke,

"Who are you?"

She demanded in an unpleasant tone.

"We could ask you the same thing."

Jace remarked to her in a similar tone as he pulled out his Stele.

**CLOSING STATEMENT :** I hope you enjoyed the second chapter, reviews mean a continuation of this story. so please review / comment and i will surely continue.


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